This invention relates to a combination electrolysis cell sealing means and separator holding means for a filter press type electrolytic cell, and more particularly, to a combination electrolysis gasket member and membrane holding device for use in filter press type electrolytic cells.
Electrolytic cells of the filter press-type are known to be used for the electrolysis of aqueous salt solutions and have been commercially employed for the production of chlorine and caustic from brine. The filter press type electrolytic cell for electrolysis of an aqueous salt solution commonly employ a plurality of frame members with electrodes held thereto and assembled in filter press type arrangement, separated from each other by membranes, diaphragms or microporous separators, forming a plurality of anolyte and catholyte compartments. The electrodes used in the cells are generally either monopolar or bipolar electrodes.
Membranes typically used in the cells are generally available in sheet form and have ion exchange properties, for example the membrane material employed in the cells are such as those marketed by E.I. duPont de Nemours and Company under the trademark Nafion.RTM. and by Asahi Glass Company Ltd. under the trademark Flemion.RTM..
Typically, a press means is used to compress or clamp together the separators in sheet form between the sides of the frame members of the filter press cell and electrolyte is used to fill the compartments of the cell. Typically, to provide a fluid-tight seal between the frame members and the separator without damaging the separator, the electrolytic cells employ substantially flat, solid gaskets having a rectangular cross-sectional area or tubular type gaskets having a circular cross-sectional area made of elastomeric material. One or two gaskets can be used to fit between the cell frame members on a peripheral flange portion of the frame members and on either side of the membrane. While most gaskets, for the most part, can provide a liquid-tight seal, the seal is generally not completely fluid-tight, i.e. liquid and gas-tight. To some extent fluid and gas seepage occurs at the interface formed between the membrane contacting the gasket members.
The problem of fluid seepage occurs particularly in cells which employ membrane separators that utilize a support or reinforcement material in the membrane. This reinforcement material is usually used because it provides a normally weak membrane with additional strength for handling and installing into industrial size membrane filter press electrolytic cells. A problem associated with the use of a support or reinforcement in membranes is that the reinforcement allows gases and liquids to seep from the inside of the operating cell to the exterior. This seepage can cause severe damage to the outer surface of the cell peripheral surface. Fluid seepage can also expose operating personnel to potentially hazardous chemicals. The problem of fluid seepage is aggravated by the use of pressurized cells operating under an internal electrode compartment pressure. The contemporary compression-seal means now being used by industry cannot significantly block the leakage of the liquids and gases in the electrolytic cells.
Another problem associated with the use of conventional gasketing of filter press cells is membrane drying. In a conventional membrane filter press type cell operation, the membrane is usually extended past the periphery of the cell and exposed to the environment. This exposure, in time, allows the membrane to dry and possibly crack. Any cracks formed in the exposed surface of the membrane can propagate, during operation of the cell, through the membrane to the portion of the membrane which is inside the cell, i.e., the operating area of the membrane, which in turn, can cause severe operation problems such as mixing of electrolytes that can cause corrosion of the cell's components or mixture of gases which can lead to explosions. Each situation can lead to the termination and eventual shutdown of the cell operation.
Still another problem associated with the assembly of filter press cells is, in addition to conventional gasketing, a separate and independent tentering device is normally needed to planarly dispose the membrane between the frame members of the cell. One conventional method of tentering the membrane involves personnel holding the membrane by hand between cell frames and stretching the membrane as the cell frames are compressed together. The cell gaskets in this instance are glued or taped to one of the electrode frames. In another method, the cell frames, membranes and gaskets are assembled in the horizontal position to ensure a planar placement of the membrane and gaskets, and thereafter standing the assembled cell in the upright position for operation. Still another method, the membrane and gasket are glued or taped to the cathode or anode frame prior to assembling the elements of the cell together. These approaches are unsatisfactory as they present time consuming, complex procedures, costly equipment and safety hazards to personnel. These procedures may also allow the membrane to dry and crack and thereby render it unfit for operation.
It is, therefore, desired to provide a means suitable for sealing an electrolytic cell and tentering an electrolytic separator to reduce the complexity of assembling the elements of an electrolytic cell.
It is further desired to provide a solution to the above problems by providing a device and method for insuring that the outer boundaries of a membrane stay in a moist or wet state and by providing a device and method for containment and/or control of gas and liquid seepage from the internal cell structure at the membrane/gasket interface of a membrane filter press type cell.